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Donald F. McNeill1, Laura A. Guertin2
(1) RSMAS-University of Miami, Miami, FL
(2) Mary Washington College, Fredericksburg, VA

Abstract: Themes Applicable for Comparative Sedimentology of the Subsurface Carbonate-Siliciclastic Mixed System of South Florida to Reservoir Distribution in Ancient Deposits

A recent drilling project to evaluate the Neogene mixed-system of South Florida has provided insight on the depositional controls and facies patterns that comprise this heterogeneous carbonate-siliciclastic sedimentary system. Four underlying themes have emerged that have implication for reservoir development and facies architecture. These “modern” themes are likely applicable to reservoir distribution in ancient mixed systems.

The comparative themes include: 1) Concept of Template Control on Both Carbonate and Siliciclastic Deposition:precursor topography controls depositional geometry and location of subsequent depocenters for both carbonates and siliciclastics; 2) Distal Transport of Coarse Clastics and Influence of Currents on Grain-Size Segregation:conditions can exist for the transport (fluvial?) of extremely coarse siliciclastics (flat pebble quartz in this modern example) long distances from the source area; and regional currents help segregate grain sizes and partition grain types; 3) The Mixing Transition: Close Proximity But Distinct Lateral Lithofacies Variation:the lateral transition of carbonates to siliciclastics highlights the potential for abrupt facies changes both laterally and vertically. A shifting facies boundary may form a subtle stratigraphic trap based on lithologic differences, while the lateral transition between the two facies would produce, in core, a subsurface section of alternating reservoir pay zones and relatively tight intervals; and 4) Recognition of a Subtle Sequence Boundary in Shallow Marine Siliciclastics:the shallow-water nature of mixed systems may make the recognition of features indicative of a sequence boundary inherently difficult. Identification of a subtle sequence boundary in outcrop, core, and cuttings may require integration of the litho-, bio-, and chemo-stratigraphic markers.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana